Implantable neural electrode

ABSTRACT

An electrode for establishing electrical contact with nerve tissue. The electrode is chronically implantable. The outer substrate of the electrode is a semi-rigid, body compatible, insulating material such as a chronically implatable polymer. The outer substrate is molded as a single structure having a central spine along the longitudinal axis of the electrode. A plurality of fingers extend orthogonally from the central spine, and are bent circularly about a radius of curvature approximating that of the nerve to be contacted. Each of the plurality of fingers is of sufficient length to extend approximately one-half of the distance around the outer circumference of the nerve tissue. The plurality of fingers extend from the central spine in one of two opposite directions causing the electrode structure to encompass a hollow cylinder having an inside diameter the same as the nerve. Because the plurality of fingers are not attached to each other, but to the central spine only, and the fingers are semi-rigid, the diameter of the hollow cylinder encompassed by the electrode structure can be readily increased by spreading the fingers during the implantation procedure. Also the diameter of the electrode is expandable to accommodate any swelling of the nerve tissue following implant. The inside surface of the encompassed cylinder is rendered conductive by the bonding or attachment of a conductor to the fingers and/or the central spine. An insertion tool spreads the fingers during the implant procedure and permits a minimum of exposure of the nerve tissue.

CROSS REFERENCE OF CO-PENDING APPLICATIONS

This application is related to Ser. No. 07/446,865, filed Dec. 6, 1989, now U.S. Pat. No. 5,031,621 entitled "Nerve Electrode with Biological Substrate"; Ser. No. 07/483,455, filed Feb. 22, 1990 entitled "Steroid Eluting Cuff Electrode for Peripheral Nerve Stimulation", and Ser. No. 07/536,524 filed June 7,1990 entitled "Tool for Implantable Neural Electrode", all of which are assigned to the assignee of this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to implantable medical devices, and more particularly, relates to electrodes for electrically coupling to nerve tissue.

2 Description of the Prior Art

The use of electrodes to monitor electrical activity and stimulate body tissue is quite old. U.S. Pat. No. 1,662,446 issued to R. H. Wappler teaches an early electrode system. The Wappler electrode is used for acute stimulation only, and is not implantable.

An early stimulation electrode which is chronically implantable is taught by S. I. Schwartz, et al. in U.S. Pat. No. 3,421,511, herein incorporated by reference. U.S. Pat. No. 3,654,933 issued to Hagfors, herein incorporated by reference, teaches an improved stimulation electrode for chronic implantation. Clinical experience with the electrodes taught by Schwartz et al. and Hagfors has shown a potential for excess irritation in certain applications. This irritation results in swelling of the nerve tissue which is exacerbated by the fixed diameter of the cuff of each device after being sutured into place.

U.S. Pat. No. 3,738,368 issued to Avery, et al., U.S. Pat. No. 3,774,618 issued to Avery, and U.S. Pat. No. 3,955,560 issued to Stein, et al. all teach electrodes having fixed diameters after chronic implantation. These electrodes also tend to cover relatively large areas of the nerve tissue, thus depriving nutrient access to great numbers of adjacent nerve cells.

U.S. Pat. No. 4,573,481 issued to Bullara suggests a neural electrode array having a serpentine shape. This shape provides significant access to nutrients by the nerve. This structure, however, provides difficulty in implantation. Because an increase in diameter of the electrode system requires a decrease in length, it is anticipated that the Bullara electrode system does not provide a satisfactory solution to the problem of nerve swelling.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of prior art neural electrodes by providing a structure which has a readily expandable cross sectional diameter after chronic implantation. This permits the nerve tissue to swell without increased irritation. The desired result is provided by an electrode structure molded of a semi-rigid polymer having a central spine with a plurality of orthogonal curved fingers. The fingers are not attached to one another to permit the diameter to vary. Enhanced nutrient access is provided by the large open surface area. The implant procedure is easily accomplished by spreading the fingers and sliding the outer substrate over the nerve tissue.

The inner surface of the fingers is provided with a conducting foil. This foil is coupled proximal to the electrode by conductors positioned along the central spine.

The implantation procedure is greatly simplified through the use of an implantation tool having a proximal handle and a distal channel. The distal channel has a radius of curvature significantly greater than the radius of curvature of the nerve tissue. Mounting the electrode structure on the outer surface of the distal channel causes spreading of the fingers to permit the combination to be easily slipped over the nerve. Curvature of the distal channel enables implantation with a minimum of exposure of the nerve tissue.

The combination is placed over the nerve tissue. The proximal handle is pulled proximally while the electrode structure is held causing it to be slid from the distal end of the distal channel. The memory of the semi-rigid fingers tends to keep the electrode system in place along the selected nerve.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects of the present invention and many of the attendant advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a perspective view of the structure of a neural electrode system employing the present invention;

FIG. 2 is a top view of the preferred mode of the present invention;

FIG. 3 is a bottom view of a preferred embodiment of the present invention;

FIG. 3A is bottom view of an alternate embodiment of the present invention;

FIG. 4 is a side view of the implantation tool;

FIG. 5 is a top perspective view of the implantation tool;

FIG. 6 is a side view of the implantation of the electrode system using the implantation tool; and,

FIG. 7 is a perspective view of an alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a perspective view of a neural conductor or electrode system 10 employing the present invention. The outer substrate or insulating structure is molded of a semi-rigid biocompatible polymer material. It has a longitudinal element or central spine 12 which is along the longitudinal axis of the electrode system. Fingers 14a-14n extend from central spine 12, and curve in a first direction as shown. Similarly, circumferential elements or fingers 16a-16n extend and bend in the opposite direction. Central spine 12, along with fingers 14a-14n and fingers 16a-16n, are molded as a single piece.

The radius of curvature of fingers 14a-14n and fingers 16a-16n are established to snugly, but not too tightly, fit around the nerve to receive the implant. Because the fingers are molded of a semi-rigid polymer, they can be spread to permit implantation over the nerve and return to the original shape for chronic use. The fingers are staggered and not connected at the ends as is described in further detail below.

Electrical contact is established using a strip of conducting material placed inside one or more fingers. In this embodiment, electrode element or metallic foil 18a is used on the inner surface of finger 14a, for example. Metallic foil 18a is electrically coupled to the proximal end of electrode system 10 (and hence an electronic circuit not shown) using conductor 22a. In the preferred mode electrode lead-in or conductor 22a is vacuum deposited to the inner surface of central spine 12 as shown in the phantom view.

Also in the preferred embodiment, fingers 14b-14n contain metallic foils 18b-18n coupled to conductors 22b-22n. Similarly, metallic foils 20a-20n are positioned on the inner surfaces of fingers 16a-16n and coupled to conductors 24a-24n, respectively. Having electrically isolated metallic foils permits the pulse generator electronic circuitry to provide stimulation according to a large number of varying patterns. Alternatively, one or more of the metallic foils may be electrically common to one another rather than electrically isolated.

FIG. 2 is a top view of the outer substrate of electrode system 10. Fingers 14a-14n are attached orthogonal to central spine 12, and curve under as shown. The length of fingers 14a-14n is chosen to extend about one-half way around the nerve to receive the implant. As can be seen distal tips 26a-26n represent the free ends of fingers 14a-14n, respectively.

Fingers 16a-16n are of equivalent length to fingers 14a-14n, and extend from central spine 12 in the opposite direction as shown. In the preferred embodiment, fingers 14a-14n are staggered from fingers 16a-16n as shown. Fingers 16a-16n terminate in distal tips 28a-28n, respectively. The spacing between fingers may be varied to accommodate the different applications for the present invention.

FIG. 3 is a bottom view of the preferred embodiment. All components are as previously described.

FIG. 3A is a bottom view of an alternative embodiment of electrode system In this mode fingers 15a-15n are not staggered from fingers 17a-17n in attachment to central spine 13. This differs from the preferred mode in that spreading of the fingers results in no overlap at all, and therefore greater nerve surface area for nutrient access.

FIG. 4 is a side view of implantation tool 30. It has a handle 40 (only partially shown) which is held by the implanting physician. Handle 40 is coupled via rod 36 to distal channel 32, which is a channel opening downward. The radius of curvature of distal channel 32 must be greater than the diameter of the nerve to receive the implant. Similarly, the opening at the bottom of distal channel 32 must be wider than the diameter of the nerve to receive the implant (see also FIG. 5). The portion of distal channel 32 which is distal to rod 36 must be at least as long as electrode system 10 such that electrode system 10, with its fingers spread, fits completely over distal channel 32.

During implantation, it is desirable to expose only the minimum amount of nerve surface. To assist in implantation, distal channel 32 is curved at bend 34. This permits heel 38 of distal channel 32 to be directed away from the implant site.

FIG. 5 is an perspective end view of implantation tool 30 disposed over nerve 50. Note that distal channel 32 conveniently slides over nerve 50. Electrode system 10 has its fingers spread to enable it to be positioned on the outer surface of distal channel 32.

FIG. 6 shows electrode system 10 as partially implanted around nerve 50 using implantation tool 30. The implantation will be completed as distal channel 32 is slowly removed and electrode system 10 is held in a fixed position with respect to nerve 50. As fingers 14a-14n (and fingers 16a-16n, not shown) are slid from the distal end of distal channel 32, they tend to resume their original cylindrical shape about nerve 50. The diameter of the resulting cylinder may be chosen at manufacture to fit loosely or snugly about nerve 50 as medical requirements might dictate.

FIG. 7 is a perspective view of an alternative embodiment of the present invention. In this embodiment, neural electrode 100 has a longitudinal element or central spine 112. Circumferential elements or fingers 116a-116n are all attached to the same side of central spine 112. As with the previous embodiments, electrode elements or metallic foils 118a-118n may be electrically isolated and have separate electrode lead-ins or conductors 122a-122n, respectively, to permit sophisticated stimulation patterns. Electrically combining these permits ease of construction though providing less flexibility.

Having thus described the preferred embodiments of the present invention, those of skill in the art will be able to apply the teachings found herein to other embodiments without deviating from the scope of the claims hereto attached. 

I claim:
 1. An electrode system for coupling neural tissue to an electrical circuit comprising:a. a central spine of an electrically insulating material; b. a plurality of semi-rigid fingers of an electrically insulating material orthogonally attached to said central spine and curved about the same radius of curvature as said neural tissue wherein each of said plurality of semi-rigid fingers has an inner surface and wherein each of said plurality of semi-rigid fingers has a length less than a circumference of a circle having said same radius of curvature; c. an electrical conductor positioned on said inner surface of a one of said plurality of fingers; and d. means electrically coupled to said electrical conductor for electrically coupling said neural tissue to said electrical circuit.
 2. An electrode system according to claim 1 wherein said plurality of semi-rigid fingers are molded with said central spine as a single piece.
 3. An electrode system according to claim 2 wherein a first number of said semi-rigid fingers are attached to a first side of said central spine, and a second number of said semi-rigid fingers are attached to a second side of said central spine.
 4. An electrode system according to claim 3 wherein said plurality of said semi-rigid fingers each have a length about one-half of the circumference of said same radius of curvature as said neural tissue.
 5. An electrode system according to claim 4 wherein each of said first number of said semi-rigid fingers are staggered with respect to said second number of said semi-rigid fingers.
 6. An electrode for mounting on a nerve comprising:a. a generally cylindrical body comprising a longitudinal element and a plurality of flexible circumferentially directed elements mounted on the longitudinal element for forming said generally cylindrical body where each of said plurality of flexible circumferentially directed elements has a length less than the circumference of said generally cylindrical body; and, b. means mounted on the circumferential elements for delivering electricity to a nerve.
 7. The method of stimulating a nerve with an implantable electrode comprising:a. providing an electrode having curved flexible fingers; b. spreading the fingers to form a longitudinal opening for receiving the nerve; c. placing the electrode over the nerve and releasing the fingers to form a generally cylindrical shape around the nerve wherein said generally cylindrical shape is not completely enclosed; and d. supplying an electrical signal to said electrode to stimulate said nerve. 